July 2017

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July 2017

Precipitation, relative humidity and soil moisture for July 2017

The surface hydrological variables are more difficult to observe and analyse than surface temperature. The surface hydrological variables page explains more about the reliability of the data and information presented here, including comparisons with alternative datasets. The data on soil moisture is currently of qualitative rather than quantitative value. This summary is intended to provide European and near-global views of conditions for the month. Specific information for many countries can be found on the websites of their weather or climate services.

Anomalies in precipitation, the relative humidity of surface air, the volumetric moisture content of the top 7 cm of soil and surface air temperature for July 2017 with respect to July averages for the period 1981-2010. The darker grey shading denotes where soil moisture is not shown due to ice cover or climatologically low precipitation. Source: ERA-Interim. (Credit: ECMWF Copernicus Climate Change Service) Download the original image

July 2017 was drier than the 1981-2010 average over south-western and central Europe, in terms of surface atmospheric relative humidity and the moisture content of the soil. Temperatures were also well above average over this part of the continent. Precipitation shows a more mixed situation; monthly totals at this time of year can be influenced by single severe events such as occurred mid-month in Greece in July 2017. Northern Germany also experienced heavy rainfall and flooding during the month. July 2017 was generally relatively cool and wet over northern Europe, but extremely dry and warm over the far north-west of Russia, as was the case also in the summer of 2016.

Anomalies in precipitation, the relative humidity of surface air, the volumetric moisture content of the top 7 cm of soil and surface air temperature for August 2016 to July 2017 with respect to 1981-2010. The darker grey shading denotes where soil moisture is not shown due to ice cover or climatologically low precipitation. Source: ERA-Interim. (Credit: ECMWF Copernicus Climate Change Service) Download the original image

Precipitation over Europe was most below average for the last twelve months over France and northern Spain. Relative humidity and soil moisture were also relatively low in this region, and temperature was relatively high. The north-east of the continent was a little wetter than average. Conditions were mostly dry over the east of the continent and the Middle East. More rain than usual fell over Greece and the central Mediterranean.

Anomaly in precipitation, the relative humidity of surface air and the volumetric moisture content of the top 7 cm of soil for July 2017 with respect to July averages for the period 1981-2010. The darker grey shading denotes where soil moisture is not shown due to ice cover or climatologically low precipitation. Source: ERA-Interim. (Credit: ECMWF Copernicus Climate Change Service) Download the original image

Rainfall in July 2017 was much above average over parts of southern Asia. Heavy rain also occurred over the south-western USA and north-western Mexico. Conversely, it was much drier than average over Mongolia and northern China, where the worst drought on record had already been reported in June. Conditions were also predominantly dry over the extratropical land masses of South America.

Anomalies in precipitation, the relative humidity of surface air and the volumetric moisture content of the top 7 cm of soil for August 2016 to July 2017 with respect to 1981-2010. The darker grey shading denotes where soil moisture is not shown due to ice cover or climatologically low precipitation. Source: ERA-Interim. (Credit: ECMWF Copernicus Climate Change Service) Download the original image

Averages for the past twelve months show particularly dry conditions over the south-eastern USA, over a region covering Mongolia, south-eastern Russia and north-eastern China, and over eastern Brazil and north-eastern Australia, for all three variables. South Africa also shows up as particularly dry in terms of relative humidity. Relative humidity was also low over much of the Middle East and north-eastern Africa, although the south of Saudi Arabia had above-average rainfall and correspondingly above-average relative humidity over the past twelve months. Canada and southern Asia were generally wetter than average.

Monthly anomalies with respect to 1981-2010 in the relative humidity of surface air averaged over all and European land areas, from January 1979 to July 2017. The darker coloured bars denote the July values. Source: ERA-Interim. (Credit: ECMWF Copernicus Climate Change Service)Access to data Download the original image

Relative humidity averaged over all land areas declined quite sharply from the late 1990s to the mid 2000s. It had fluctuated around a quite uniform level prior to that, and has fluctuated around a lower level over the past eleven or so years. July 2017 had the lowest average relative humidity of any July in this data record.

Relative humidity averaged over Europe is more variable, but also shows a net decline over time. Corresponding time series of soil moisture show a similar drying.

This drying is not accompanied by an appreciable reduction in precipitation, as shown below for Europe. It may be a consequence of a period in which surface air temperature rose faster over land than it did over sea. Continued monitoring is required to document behaviour over a longer period and refine the understanding of this aspect of climate variability or change.

The variation over time of the hydrological variables and temperature are shown below for averages over NW, NE, SW and SE Europe. Values are also averaged over successive four-month periods, to enable variations on upwards of the seasonal time scale to be seen more clearly than if monthly values had been plotted.

Regional differences are quite pronounced in the time series. Average precipitation rates are higher in the north, particularly the NW, but precipitation is more variable in the southern regions. The latter can also be inferred from maps of the variance of monthly precipitation, so is not simply a consequence of the smaller areas of the southern regions or the four-month averaging. Warming is largest in the NE, but the decrease in relative humidity is larger in the south. The correlations between precipitation, relative humidity and soil moisture evident in the maps of anomalies can be seen to hold for the area averages on time scales up to a year or more, but precipitation does not show the marked longer-term decrease seen for relative humidity and soil moisture.

The four months to July 2017 are notable for SW Europe, as they have the lowest anomalies in relative humidity and soil moisture of any four-month period in this data record. The four-month temperature anomaly of 1.9°C is the second highest on record for the region, exceeded only by the average of 2.0°C for the four months to June 2017.

Running four-month averages of anomalies over NW Europe with respect to 1981-2010 for precipitation, the relative humidity of surface air, the volumetric moisture content of the top 7 cm of soil and surface air temperature, based on monthly values from January 1979 to July 2017. Source: ERA-Interim. (Credit: ECMWF Copernicus Climate Change Service)Access to data Download the original image

Running four-month averages of anomalies over NE Europe with respect to 1981-2010 for precipitation, the relative humidity of surface air, the volumetric moisture content of the top 7 cm of soil and surface air temperature, based on monthly values from January 1979 to July 2017. Source: ERA-Interim. (Credit: ECMWF Copernicus Climate Change Service)Access to data Download the original image

Running four-month averages of anomalies over SW Europe with respect to 1981-2010 for precipitation, the relative humidity of surface air, the volumetric moisture content of the top 7 cm of soil and surface air temperature, based on monthly values from January 1979 to July 2017. Source: ERA-Interim. (Credit: ECMWF Copernicus Climate Change Service)Access to data Download the original image

Running four-month averages of anomalies over SE Europe with respect to 1981-2010 for precipitation, the relative humidity of surface air, the volumetric moisture content of the top 7 cm of soil and surface air temperature, based on monthly values from January 1979 to July 2017. Source: ERA-Interim. (Credit: ECMWF Copernicus Climate Change Service)Access to data Download the original image